INDIANAPOLIS — Bill Bradley is a Knicks legend and former U.S. Senator and now an admitted former ball doctor.

Bradley told The Post in a phone interview Thursday he used to regularly deflate basketballs — but only when he felt they were above specifications and overinflated.

Bradley, whose nickname was “Dollar Bill,” said he performed his ball magic before and during games. He said he believes referees knew what he was up to but didn’t care.

Bradley’s remarks come in the wake of the resurfacing of Phil Jackson’s 1986 quotes in which he said the Knicks’ 1973 championship team deflated balls to gain a competitive edge. It prevented long rebounds as the club was undersized up front. Jackson tweeted Wednesday it was not illegal and the balls still met specifications.

However, Bradley told The Post he didn’t have an official gauge and used “my hands’’ to judge whether the ball met NBA regulations. Deflating balls became a hot button issue after the Patriots were allegedly caught doing so in the AFC Championship Game.

“This is the story — I wanted to make sure the ball was not overinflated,’’ Bradley said. “You’d get balls overinflated at which point I’d take the air out. I have shot enough to know the feel of the ball. If it was overinflated, I took some air out. Three-quarters of the time, it was no problem. Twenty five percent of the time, the ball was overinflated.’’

Bradley said former trainer Danny Whelan would give him the balls to inspect before games.

“I took a needle and took the air out,’’ Bradley said. “If you’re players and shoot as much as you have to shoot, you’re going to know and you can tell when the rim is a half-inch low also. It’s a feel. I’ve shot millions of shots. I know how the ball feels. If I get it and it was overinflated, I’d try to correct it.’’

The current NBA bylaws state the ball has to be between 7.5 and 8.5 pounds per square inch. NBA officials have told The Post the specifications in the late 1970s were likely the same, though they can’t confirm that. Jackson tweeted the Knicks would deflate the balls down to seven pounds. Marv Albert said Wednesday he recalls seeing Bradley with a needle in the huddle working a ball.

Exactly what weight to which he deflated the ball Bradley can’t say.

“I have no idea,’’ Bradley said. “But nobody ever said anything. If there was an issue, the referee would’ve said something when I gave the ball back to them. They felt the ball. From my perspective, they saw me do it.’’

Bradley would not acknowledge what Jackson has — that it gave the Knicks a competitive edge. The balls were the same for both teams. Bradley added it was his personal preference.

“It’s a softer ball on the rim,’’ Bradley said. “A heavily inflated ball bounces back to the foul line and you never get any bounces around the rim that go in.’’

According to Bradley, coach Red Holzman never ordered him to deflate balls.

“I didn’t want them overinflated, it bothered me,’’ Bradley said. “It wasn’t a team decision. It was my decision. I don’t think anybody ever discussed it — just with Danny Whelan.’’

Asked about the hubbub over the Patriots, Bradley, who once ran for President, said, “Ludicrous. When I read that story, I was like how is this a story. It’s not even a story. I think it’s blown up to have stories to have before the Super Bowl.’’

Bradley has been Jackson’s unofficial consultant and occasionally offers player evaluations. Jackson’s first full season as Knicks president has been a disaster, with the Knicks likely to finish with the worst record in franchise history despite a recent upturn after Jackson’s fire-sale trade.

“It’s a tough year,’’ Bradley said. “You just have to get the right players. He’s boxed in right now. I have every confidence he’ll be able to do it.

“Someone who has won as much as he has doesn’t like to lose. He realizes the cards he’s been dealt and is trying to make the best of it. You have to have the right attitudes on the team — team guys, team players. Then you get guys with talent so they can play their roles.’’

Asked about the evaluations he’s given to Jackson, Bradley said, “I’ve learned from politics, when you advise the president, you don’t reveal the specifics.’’